This invention relates to an automatic flesh correction circuitry for a color television receiver.
Reproduced colors of a color television receiver are often distorted due to signal transmission line distortions, a variation of characteristics of a color television camera, a variation of illumination in a studio and so on. For this reason, viewers often have to adjust a color television receiver to get good pictures. Therefore, it is very important to automatically reproduce desired colors matched to human visual memory, because viewers will not tolerate bad flesh tones.
To acquire desired flesh reproduction with less adjustment, several kinds of flesh correction systems have been proposed. One is a VIR (vertical interval reference) control system which corrects color signals with reference to VIRS (vertical interval reference signals) inserted in a vertical interval of a transmitted signal. This system is very useful if VIRS has adequate information with respect to the transmission line distortions. But, when the VIRS itself is unreliable, its use will increase color reproduction errors in comparison with those occuring without VIRS.
Another flesh correction system is a phase correction system which modulates a subcarrier phase referring to a phase difference between a subcarrier and a carrier chrominance signal. This system comprises a subcarrier generator for generating a subcarrier whose phase corresponds to I axis, a phase detector for detecting a phase difference between the subcarrier and the carrier chrominance signal, an adder for adding the subcarrier and the carrier chrominance signal, a phase shifter of an output signal of the adder, a chrominance decoder for decoding chrominance difference signals, I and Q, from the carrier chrominance signal, using an output signal of the adder and an output signal of the phase shifter. In it, a subcarrier phase is modulated by an output signal of the phase detector, whereby this system controls a decoding phase of the chrominance decoder when a carrier chrominance signal phase is in the vicinity of the flesh tone phase. It is clear that this system stabilizes a hue of a reproduced color and pulls a transmitted color into the flesh tone. However, as this system changes a decoding phase of a chrominance decoder in the vicinity of a flesh tone, it inherently distorts the transmitted signal and this distortion is, very noticeable in highly saturated green, magenta or red. For example, a green tree becomes a yellowish dead tree.